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Why do Electric Aircraft Seem to Eschew Photovoltaics?
I work in climate policy so I'm always excited for things that could help me feel less guilty about being into aviation such as biojet and the progress being made in electric propulsion.
To date, however, all of the examples of electric aircraft that I've seen lack photovoltaic equipment (i.e. solar panels). Given the concerns with electric propulsion seem to stem from a lack of energy/power density in current generation battery technology, this feels like a glaring omission.  Any amount of PV (sunk into the top of the wings, for example) would produce positive power and mitigate consumption of stored energy in batteries - even on cloudy days.
It's obvious that the systems are nowhere near sufficient to power flight, but given how on-the-margin electric propulsion operates it feels like low hanging fruit from an electrical power perspective.  You'd gain the operational benefits of refueling anywhere you could park it in the sun for long enough (to be fair, that'd likely take a LONG time).
I assume there's technical reasons to eschew the equipment, but I'm curious what the constraining factor(s) are, specifically.
The candidates I can think of up front are weight (silicon wafer isn't that heavy, plenty of PV can be made extremely lightweight and you need the wing to be rigid already so balance of structure isn't adding much, if anything), volume (silicon wafer is, pardon me, 'wafer thin'), technical complexity (this is an experimental aircraft we're talking about, remember) or cost (see previous) - all of which seem readily dismissed.
EDIT: I'm not asking about PV as primary power, I'm asking why engineers are leaving 'money on the table' as it were, by not including PV in battery-primary designs.
What am I missing?

Solar panel flowchart: https://xkcd.com/1924/

For clarity, by "electric aircraft" did you mean drones, or normal-size novelty experimental aircraft??

Whatever you put in the top of the wings must not interfere with the air flow that allows the wing to provide lift.

@Fattie The latter.

@David K - Yes, I'm talking about sinking the PV into the top surface of the airfoil as an integrated part of the wing's design, not crudely strapping something down with duct tape.

@WilliamWalkerIII I'm afraid that it clearly seems to be wildly outside the bounds. But one thing that comes to mind. There was a BM? Mercedes? model car where, ok so for on really hot days, obviously cars have fantastic air coinditioners when running. For sunny climes, you park for 20 minutes while buying your latter (at the mall I guess!) and of course the interior of the car is holy heck hot. Cracking the windows helps but is illegal/etc insecure in some places. Companies tried small exhaust fans ie run by the normal car battery but its not a reliable idea to use that battery. So, there wer

e 1 or 2 models which had (naturally as a paid optional extra :) ) basically the sunroof or some relaticvely large area oin the roof, was a solar panel, that drove some sort of "for when you are parked" cooling system for the car (it was probably just exchaust circulation fans, but maybe some sort of cooling, IDK.   Perhaps this kind of "incidental" use of panels could be relavent to what you're thinking.  PS if I'm not mistaken in a comment below, you mention that you were not aware! there are literally experimental extreme planes which fly using entirely solar power, this perhaps causes

some confusion on this QA.  Cheers!  I love solar power for the rare applicaton where it's useful, but it's incredibly "weak" you know?  :O

@Fattie When you're full electric those issues end up blurring together due to oversimplification.  Given the discussion thusfar it's looking like the answer is going to be some combination of 'every gram matters' and 'complexity raises cost and the add-on benefit doesn't justify that yet.'

@WilliamWalkerIII absolutely, I was talking about PETROL POWERED cars (those models were from way before the Tesla era). Your question is about PETROL POWERED planes, using, solar for "incidental" issues.  So i thought it was an interesting example.  (BTW planes will ONLY ever be "petrol powered", nothing else has the fuel density. The only possibility is nuclear power (fusion, fission, whatever) but it's very very unlikely that will ever be possible, as a light enough reactor, to beat petrol for energy density, is a sci-fi idea, made of unobtanium.

@Fattie I am not talking about petrol powered planes. I'm talking about fully electric aircraft such as a Archer Midnight, or Pipstrel Velis Electro.

@WilliamWalkerIII  'every gram matters' and 'complexity raises cost and the add-on benefit doesn't justify that yet.' i feel you're fully missing the far more obvious third option there.  the stunning, mindboggling, just UTTERLY INSANE amount of power that an airliner (big plane) produces just utterly, utterly dwarfs both (a) the "incidental" needs you discuss and indeed (b) what could be created by solar panels.  I'm not sure if you're aware, the big engines on big aircraft have (to summarize) stuck on them "merely" as an incidental matter pretty big electric generators which provide the enor

mous amount of electric power used by a big plane in flight, the enormous number of microwave ovens, 400 large TV sets, headlights, etc etc.  Anyway.

@WilliamWalkerIII "Archer Midnight, or Pipstrel Velis Electro" lol OK I've finally got you.  those are novelties that don't matter, but again (not saying anything novel)  it is "option three", the amount of "bonus power" you're talking about is simply irrelevant compared to the ginormous battery.  I'm afraid it's not your option 1 or 2, it's 3

@Fattie You seem to have a very negative view of innovation. If everyone in history felt that way, the only vehicles we would have would still be sandals. Energy densities are continually increasing and new motors are consuming less power. There are already commercial electric planes nearing production, so why dismiss a minor improvement.

@Suncat2000 I'm sorry to disagree! Solar panels are useless and, indeed, anti-innovation.  If you frame the viewpoint "solar panels are useless" as "anti-innovation" that's  ingenious debate wordplay, I'm afraid.

@Fattie "solar panels are useless" answers this question, and I don't see anything so strong said in the existing answers.  Perhaps add your own?

Standalone recharge anywhere... As said, the wing surface is too small, the aircraft will likely get grounded several days... Why not just put an array of solar panels finely calibrated for efficiency at many airfields ? Charge would complete fast, and work for a broad variety of aircraft size, ground vehicles and equipments ? The ground array would be easier to maintain and upgrade.
Wings aren't rigid ! Common misconception is "it has internal structure, therefore, it will remain straight..." Actually, over a couple meters, a wing bends. At microscopic level, it slowly deteriorates over time (wrincles/cracks). A layer of solar panels will rub the wing surface at contact level, especially along the edges and at the corners (is it glued or what ?). That's a technical issue, how often it has to get fixed to keep that upperwing clean (ie no aerodynamical disturbance) ?
Weather ! I know solar panels can be reinforced to withstand hail. In aviation, this translates to weight and extra costs. That's usually a big NO.
Efficiency. Solar panels lose efficiency with dust and scratches (we ignore the other causes to focus on those). Snow, dust, rain, hail... Even if it's just for supplement purposes, it has to be maintained well to have a meaning : how much hassle to care for ? What to do before each flight, what to do between flights ? What could go wrong if not properly handled ? Practically, the amount of care is much concerning than adding another battery, as mentionned.
Maintainance : One way to gain or lose money in the aviation industry is how much of a cost is maintaining engines and systems. Who's (company/subcontractors) in charge of ensuring maintainance of those solar panels ? If it's a small company only present in a few states in the US... You either need a company that can handle problems whatever the country, or a company that can qualify personnel, or a company that uses OEM components any developped country can produce (and not charge too much for patents...) - likely a combination of those.
Please rest assured I'm not here to discourage all efforts in building environmental friendly systems, components and behavior, but for practically everything, the purpose must have a meaning. An aircraft is meant to move people or goods over terrain or faster than any other way. To be efficient, weight has to get "donated" to payload as much as possible instead of structure, equipment and systems (unless safety is a concern), and the vehicle has to be as less of a hassle as possible to operate (unless safety is a concern). Your question ask for the "why not" rather than the "how to", therefore, we focus on the purpose, not the technical issues that can be solved in a way or another.
Experimental aircraft are nice, but sometimes, they fail to remember what was the purpose... You can build a self sustained fully electric aircraft, but if you can't put people and cargo inside, and/or it requires special care (qualified people, frequent checks, logistics/equipements, spare parts manufacturing...) on a daily basis which translate to utterly expensive costs the end user (you and me) has to pay...
On a related yet distant topic, it's very similar to "flying cars" : the purpose is to safely transport people over cities... quite a major safety concern : how would you ensure the everyday lambda anyone is qualified enough to actually fly that thing ? That's the answer why over 2 centuries of dream, yet, the drones-like advertised vehicles are still a long way before taking off from our backyard. The purpose, it being safety and/or "economically viable", should be at the center of the design process, from the start, not a concern one solve later. For an aircraft, you freeze payload and range first (for example), then you solve every major safety issue (means a LOT of dead weight), then you solve all other problems and assert if adding solar panels is a bonus or a malus. Not the other way around.

It depends on the specific use case, but in general, it's not worth it given the alternatives. The power delivered by solar panels is too low to have a meaningful impact.
Solar irrandiance is about 1361 W/m2 (best case, at the "top of atmosphere" irradiance. The surface irradiance is roughly 1000 W/m2 due to particles etc, thanks for the comment, Mark). If we assume about 10% efficiency for thin-film cells, that leaves about 136 W/m2 or 0.136 kW/m2.
So for the Pipistrel Velis Electro, with a wing surface of 9.51 m2 -even though some of that is flaps/ailerons that cannot as easily be used for solar cells-, that would give you 0.136 * 9.51  = 1.29 kW, at best (best case irradiance, full wing surface and ignoring cable/charging losses).
Compare this with the 35 kW delivered by the engines in cruise.
This is a bit over 3%  at the price of extra costs/weight/complexity. It's probably much less trouble to add 3% (~4.2kg) batteries.

I appreciate the maths here.  Assuming we don't plan the VFR reserve around the PV being available, the Pipistrel gets better than +5% endurance under those assumptions... but that's still just over 3 more minutes so it's illustrative of the de minimis nature of the impact for sure. What's interesting to me, though, is that it suggests a breakeven point at 34% efficient PV, technically outside the SQ Limit, but not by much.

@WilliamWalkerIII, how do you end up with the breakeven point at 34%? If 10% efficient cells deliver 3% of the cruise power, you would need 30x that to break even.

By breakeven, I assumed 20% increase in range would be worth the trouble (ten more minutes on the Pipstrel, plenty for at least one more lap around the pattern). So 3x the 10% gets you enough mitigation of battery drain that you can achieve that. The relationship isn't 1:1 because the constraint is "my batteries are at VFR reserve" so delaying that state is where the value comes from.

@WilliamWalkerIII add 90kg for the panels and we've probably lost the 3% range gain. Airplane efficience is very sensitive to weight. Pipistrels empty weight is only about 300kg...

@Jpe61 I'm dubious that the panels would weigh much at all - just the mass of the wafers and wiring, maybe a tiny increase in an inverter if one is needed (I suspect electric aircraft are fully DC). The reason PV panels have mass is because they're in frames, but if you're using the wing itself as a frame, I'd expect that to no longer be necessary - unless you're saying it definitely would be necessary to add further structure to wings to accomodate such, in which case that'd be a killer as you say.

@WilliamWalkerIII you are correct in that if they were specially manufactured for this purpose, then the weight would be much less. The wafers would need some protective films so they would not be insignificant in weight in any case, if we consider light aircraft such as Pipistrel.

@WilliamWalkerIII Paint is a significant weight on an airplane. Even assuming that the weight of the cells is all the extra weight added by this change (ha!), you would still see a significant increase.

That 1361 W/m2 is the "top of atmosphere" irradiance.  The surface irradiance is roughly 1000 W/m2, give or take things like particulates.

@Mark good point, added it. Kept the answer the same as a 'best case' scenario

@ROIMaison Other factors: The additional wiring and electronics (charge controllers) add weight to a plane (specifically the Velis) that has as much weight reduction as possible, including the removal of airbrakes that are useful on its sister petrol models for landing. The wiring of the panels has to be more complex to get the best out of the panels since they don't all point the same direction, ie more weight. Finally, the first Pipistrel electric (experimental) could regen from the windmilling prop on landing, to get certified they removed it from the Velis for in flight battery safety.

It's worth noting that there are commercial thin-film cells with efficiences exceeding 20%, and research points to 30-50%. On the other hand, latitude, time of the year, time of the day and weather mean that the actual received energy may be a lot less than 1000 W/m2 (especially in the case of the Pipistrel Velis Electro which is more likely to be below the clouds than above them), so overall the end result is probably going to be much worse than the 3% you got to.

@fectin That's a solid point, but paint also doesn't generate power/reduce battery mass. But if it's a game of grams, then it becomes very understandable that pv wafers will need to become far more power dense to earn their keep.

@Mark  - and that irradiance is a maximum, at mid-day, and at lattitudes near the equator - rather lower for Europe and the USA/Canada, I believe, and at dusk/daw, never mind at night.

As you state, "nowhere near sufficient to power flight". And that includes charging.
The Airbus Zephyr 8 has a 25 meter wingspan, and the top surface of the wing is ALL solar panels. It can keep itself aloft sort of indefinitely.
Change that flying to recharging, and scale down to realistic aircraft sizes, and you'd probably have to leave it outside for a week or two, just to recharge once.

I understand what happened here. Edited the question to clarify I'm not asking why PV isn't used as the primary/sole source of power, but rather supplemental to a battery-based scheme. Upvoting for the link to the Zephyr though, that's a new one for me.

Primary power or recharging, pretty much the same. Not enough surface area to provide enough power for the recharge in any rational timeframe.

That seems equivalent to saying "Sure, we could use less fuel, but this doesn't bring fuel use to zero, so it's not worth it." If I'm paying for the kWh to recharge on the field, why wouldn't paying less for that be a desirable trait?

@WilliamWalkerIII - Cost and complexity, for no meaningful gain.

@WilliamWalkerIII: Putting solar cells on the portion of a hangar roof facing the Sun would almost certainly cost less (in both initial and ongoing costs) than putting solar cells on a plane, but reap a lot more energy.  If airfields had solar cells installed everyplace they were practical, and still needed more energy, then it might be worth considering adding them to planes, but why add them to planes if an alternative woul be in every way better?

"Edited the question to clarify I'm not asking why PV isn't used as the primary/sole source of power, but rather supplemental to a battery-based scheme" because for ancillary minor power needs, it is out by 2? orders of magnitude.  the surface area of planes would need to be 100x larger, and, of course never fly other than cloudless high noon. :)

Any amount of PV (sunk into the top of the wings, for example) would produce positive power and mitigate consumption of stored energy in batteries - even on cloudy days.

That's fallacious. Sure, any amount of PV would increase gross power, but it's hardly guaranteed to increase net power. Adding PV means increasing the weight, which means higher power requirements. PV runs at about 20W/kg. A Boeing 737 takes about 100W/kg  to stay airborne. With more efficient aircraft and PV with better power/weight ratios, you can make this work, but it's far from trivial.

You'd gain the operational benefits of refueling anywhere you could park it in the sun for long enough (to be fair, that'd likely take a LONG time).

Why fly the PV around with the plane? Why not just put PV on the roof of the hangar? It's not like first-stage electric flight is going to be flying into the middle of nowhere. Departure and destination is going to both be to places with well-developed infrastructure.

The overwhelming majority of PV's mass is from frame and inverter equipment - a full electric plane, I assume, is either DC (no inverter needed) or already has an inverter to manage the power from the battery (again, no additional inverter needed).  The structural frame is also not needed here, because the wing/body already exist.
I challenge the claim that PV is as heavy as proposed, once we already have an all-electric airframe.  I'm happy to be proven wrong, and if you can do so with documentation this'll get accepted.

Solar panels were used to power AeroViroment unmanned aircraft developed under NASA's Environmental Research Aircraft and Sensor Technology (ERAST) program.
Four of them were developed from the middle of the '80s till the end of the last century, namely the Pathfinder, Pathfinder Plus,  Centurion and Helios.
Wikipedia has a good entry about them.

It's worth noting that there are solar-powered aircraft. The linked Wikipedia article lists 11 different models/ranges of aircraft, going back to 1974.
However, the limited amount of power one can get from solar cells compared to the power required for the aircraft, means that those aircraft are very specific, and:

Have a very large surface (Zephyr 8/S has a 25 m wingspan, Solar Impulse 71.9m)
Are extremely light-weight (25 kg for Zephyr 8/S, 2000 kg for solar Impulse)
Can only carry a very limited payload (5 kg for Zephyr 8/S, one single pilot in an unpressurised cockpit for Solar Impulse 2)
Usually fly very high to get maximal solar irradiance above the clouds
Usually fly very high to avoid turbulence, as they tend to be very fragile
Are usually quite slow (Solar Impulse's average speed was 76 km/h)
Usually fly pretty long missions so the proportion of flight in cruise is maximised
Many can't even take off by themselves and need to be launched with balloons or towed by other aircraft
Are experimental and are able to achieve their objectives only in very specific circumstances (locations, weather...)

Trying to scale that to anything useful to carry passengers on "normal" flights quickly breaks down completely: if you need a 71.9m wing span for an aircraft capable of carrying only a single pilot, imagine what you would need for even a few dozen people! And even more if you want that aircraft to be as sturdy and capable of flying in nearly any weather as a conventional airliner.
The end result is that, as demonstrated in other answers, for a "regular" aircraft, the amount of power you can get from solar cells on the existing wing span is just negligible, and also extremely variable (depends on latitude, time of the year, time of the day, weather...). Compared to the added cost and complexity, it's just not worth it.
In the very best of cases (aircraft in cruise at very high altitudes, far above the clouds, in daylight, with top of the line solar cells which only exist in research labs at this time), you could get probably 500 W/m2.
A 737 requires 7.2 MW just to keep altitude and speed. If we want to achieve 10% of that power (remember, in cruise, at high altitude) using these best-of-the-line-not-available-yet solar cells, we would need 1440 m2 of wing surface, about 10 times the actual wing surface.

As a supplement to ROIMason's answer, what if we used top-of-the-line solar panels?
The Airbus Zephyr 8/S is an unmanned vehicle weighing 65 kg with a payload of 5 kg and it can fly for over a month. We can use this as an example of what top-of-the-line solar panels can do on an aircraft.

...Solar cells are high-efficiency, lightweight, and flexible inverted metamorphic multi-junction epitaxial lift-off GaAs sheets manufactured by MicroLink Devices, with specific power exceeding 1,500 W/kg and areal powers greater than 350 W/m2.

Using the example of the Pipistrel Velis Electro, its wing area of 9.5 m^2 would deliver at best 3.3kW vs the 35kW cruising power, or 10% more power. For about 2kg (plus the extra hardware).
These are top-of-the-line "call us if you want pricing" components. We can assume they're not cheap.
The endurance of the Pipistrel Velis Electro is listed at 50 minutes. Is the cost to install and maintain top-of-the-line solar panels worth an extra 5 minutes of flight time? Probably not.

What was the monetary cost of those "top of the line" panels?


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What is required for repeated use of an unimproved area for *repeated* aircraft operations?
My friend and I were talking about their new house with 7 acres in rural Massachusetts. Since I'm always shopping for excuses to log hours, I half=jokingly talked about coming out to visit if they could find a length of level grass long enough. (They assured me they could.)
This got me thinking: If they were going to build a proper turf strip out there they'd need to do a bunch of paperwork and get approvals from local entities, the FAA, and MassDOT.
All of the language therein, however, seems to be focused around building, changing, modifying, or abandoning airports.
If they never strike the earth, is there any reason to expect them to get into trouble if I fly in and out of their backyard a few times a year?
How far can you go towards facilitating bush planes flying in and out of somewhere before you need to file paperwork?

@GdD It does not. I know I can land there. But there's a difference between landing there once, and making repeated trips in and out.

No, there isn't any difference between landing there once and making repeated trips @WilliamWalkerIII, at least from an FAA point of view.

Mongo's answer in the dupe question addresses the "repeated" aspect pretty clearly, so voting to close as dupe.

The FAA doesn’t care how often private aircraft use a private field. It is completely optional to register it as an airport, though there are substantial protections if you do that make it worth filing the paperwork.
However, state/local laws vary wildly; in some places, you can’t legally land somewhere even once without it being a registered airport, while others don’t care if you do it every day. So, consult an aviation attorney for details on your specific location.

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What would be involved in disconnecting one set of controls in an aircraft?
Every aircraft I've seen has two sets of controls, even aircraft with only two seats. For any number of reasons - we'll go with "This pre-teen is super excited about aviation and wants to fly, but has motor control issues" - a pilot may find themselves with a passenger who can't be trusted to not fuss with those controls.
My understanding is that in anything that isn't fly-by-wire, those controls are mechanically/physically bound together (along with the control surfaces), so I assume there's no cutoff lever that would allow the PIC to positively assert control over the aircraft.
With that understanding, what would the process be to (legally in the U.S., and ideally reversibly) disconnect the controls for one seat?
Obviously each aircraft's mechanical specifics will vary, so the physical part of the job should be summarized but I'm interested to know if such modifications (which presumably don't meaningfully alter the weight and balance) automatically require the aircraft to be registered as Experimental and whether or not this would be mechanically straightforward or a massive undertaking.
EDIT in response to comment:
If a specific plane is required for your answer, assume a Piper J-3 Cub or some other fore-and-aft seater where a rambunctious passenger couldn't just lean over and grab the PIC's controls.  If there are specific aircraft where this is easier to effect than others, that's also interesting and should be included in an answer.

Since you seem to have a specific aircraft (type) in mind, perhaps you should tell us what airplane you want to do this in -- it's very different in a Piper Cub than a Cessna 152, for instance...

@ZeissIkon I'm not actually specifically thinking of any particular aircraft, but if there's a plane where this would be easier than most that's interesting information for me.  I'll update the question accordingly.

I personally would not mind seeing answers for different GA planes. This is an interesting question.

The PA-15 Vagabond only had 1 set of controls. It's like a Cub with side by side seats.

Highly related!  -- https://aviation.stackexchange.com/a/53864/34686

OK, what's the famous story, published in a well-known aviation autobiography, can't bring it to mind right now.  AT-6 Texan had control sticks that could be removed.  One particular instructor pilot (flying from back) was famous for signalling to students that he trusted their judgement and was about ready to let them solo, by unbolting his control stick and tossing it overboard out past the sliding canopy.  Students decided to play a joke-- hid a spare control stick in front cockpit-- when instructor threw his stick overboard, student feigned a puzzled questioning expression, then did same!

Hopefully the plane in question does not also have engine controls, fuel shutoff, avionics, etc. within reach of the untrusted person? If so, I don't think it would be wise to take this person flying if they can't be trusted to not mess with the controls. Engine suddenly quitting when pax gets excited right after plane takes off would really ruin your day.

This is at least going sideways, and is removing the second set of controls a purely mechanical issue? Isn't dual control a legal requirement for safety reasons… else why would manufacturers not offer cheaper, solo variants? Further, in a tiny little two-seater, is it certain the pre-teen passenger who can't be trusted not to fuss with the controls because of motor control issues isn't itself a safety issue? If everyone's certain only mechanics matter, fine!

@RobbieGoodwin No, dual controls are not a legal requirement (at least not in the sort of light airplanes that it sounds like OP is talking about.) They're there mostly for purposes of flight instruction. It's probably cheaper to just design and certify the plane with two sets of controls than to design and certify both dual and solo control variants. The cost of the physical extra hardware for the second set of controls is completely negligible in the context of aircraft design. These are not mass consumer products built in the tens of millions where cents matter.

Seems to me that a person should learn to obey orders of those in authority regarding life and death situations before being allowed to board an aircraft in a crew member's seat, regardless of how excited they are to do so or how young they are.  I mean, cart before the horse?

@reirab I don't doubt that facts of what you say… that this isn't a legal requirement for light aircraft, and dual controls are mostly for instruction.
At risk of being shot down off Topic, I suggest it might well be cheaper to design and certify a plane with only with two sets of controls but design and certification isn't the point; only potential profit from extended production and sales.
Won't solo- planes cost thousands less than dual-control variants?

@java-addict301 yes, a person should learn to obey orders, but not all people can do so. No malicious harm in intent is involved, but those with motor control or emotional issues may simply flail out of pure delight, causing issues when piloting an aircraft. It seems to me a better solution would be to go up in a 4-seater and put the passenger in the back where such unintentional movements wouldn't be detrimental to flight safety.

No there isn't until you get to transport category airplanes that have dual redundant control path systems, with left/right control disconnect systems, to cater to system mechanical jam cases.
A few airplanes have control yokes that can be moved to either pilot's side or the passenger's side. The DeHavilland Beaver and Beech Bonanza are like that. When the yoke is on your side, the passenger only has rudder pedals.
On most GA airplanes with dual controls, they are always connected together, so the only way to keep the passenger's hands off is to remove the control itself from the airplane, and you'll sometimes see airplanes with the right control column removed, like planes used to drop jumpers, or planes never used for dual instruction, like bush planes, so they just want the column out of the way.
On tandem airplanes like a Cub, the control stick just goes into a socket retained by a bolt or pip pin, and frequently you'll see the passenger seat's stick removed from the socket to preclude any funny business.
In the end, if you're really worried about that sort of thing, I'd worry more about a passenger in your car that waits until a truck is approaching on a 2 lane highway and reaches across and yanks the steering wheel when the time is right.  Nothing you can do about that, and it's lights out in a few milliseconds.
In the plane, you'd have more of a fighting chance, especially if you had some altitude.  And if that was to happen somehow, there is a trick I learned when instructing in gliders to deal with students that freeze on controls - you choke them, either grabbing the throat with both hands, or a little karate chop to the front of the throat.  They'll let go (fortunately I never had to actually try it).

I've always thought about a non-pilot that would instinctively hit the left rudder pedal on landing as if trying to hit the brake on a car.  Seems like a very likely scenario.

My wife does that lol. I normally brief pax to keep their feet away from the pedals.

Hopefully you don't apply John's "little trick" to her...

Somehow I've got the mental image of "Karate chop to the throat" showing up as a line item in the QRH under "panicking PIC".

Instructing in a Schwietzer 2-33, you are hunched right up behind the student and you can easily reach their neck.  Other two seaters like a Blanik or Puchatz, you can't really reach unless you release your harness.  The neck is one spot where any kind of physical disturbance you can apply will make someone instinctively let go of what they're doing and reach for it.

Many tandem two-seaters have an easily detached rear (or in some cases front) control stick.  Combine this with a simple rudder pedal cover, and a passenger is locked out of all controls other than throttle.  For aircraft built with this option, there is no regulatory effect from detaching the removable stick.
Next step up is a central stick (found in some side by side two-seaters) or throw-over yoke, most commonly seen in Beechcraft Bonanzas.  The Bonanza versions with this setup also had folding rudder pedals, so a passenger in a front seat would again have no controls other than power lever.  Built/certified this way, so FAA doesn't care what configuration you fly in (BTW, the Bonanza throw-over isn't readily switched in flight, making this version less desirable for instruction).
Plenty of homebuilt two-seaters have been constructed with single controls -- registered as experimental anyway, as long as it passed an inspection in the setup you'll be flying, good to go.
Now, if you start altering a certificated airframe by disabling or removing primary controls from the second seat, you will start to run into regulatory questions, but there are so many other options that don't require this that I'd handle it on a case by case basis -- if you own an airplane and want to take this enthusiastic disable teen on a flight, you should consult your local airframe mechanic and inspector.

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Can jet fighter missiles descend or ascend?
I am wondering that if missiles fired from jet fighters can ascend or descend?
Are they going to aim only horizontally?

Yes. Yes, they can.

Yes, they can. Air-to-Air or Air-to-Ground missiles are often equipped with little fins that allow certain maneuverability or also with thrust vectoring.

(Image Source: WikiPedia - Author: USAF)

(Image Source: WikiPedia - Author: Titimaster)

Long range missiles benefit from the lower air density at higher altitudes. Short-range missiles normally fly line-of-sight to the target, but for distances of more than 8 or 10 km, the range of the missile increases significantly if it first climbs for the cruise phase, and only descends when it closes in on the target.

Which missiles do this? I know the F14's Phoenix missiles could do this, but those were exceptionally long range missiles.

Do you have any references?

@MSalters - probably the AMRAAM missiles as well - most other western missiles are shorter range (Sidewinder, Sparrow, ASRAAM) and don't benefit since they don't have the range

Just an appeal to authority but I know the AIM-120 AMRAAM is designed to climb  after launch and descend as described. It's all about energy management; the missile keeps more of the energy it gets from its motor (which doesn't last the full 45 seconds it might take to get to its target) so it remains more energetic when it reaches the target. I think the Sparrow was designed to do this too but don't quote me on that one.

@KeithS typically anti-air rocket motor burn times are going to be measured in single digit seconds.

I am wondering that if missiles fired from jet fighters can ascend or descend?

Almost every AAM ever built can ascend, while some could descend. Every missile made today can do both. It has to do with the seeker.
With an IR seeker the target is a point source that is very strong against anything other than the sun, or sometimes the reflection of the sun off of clouds. So even if the aircraft is flying below you, their IR signature is visible and the missile can track - in fact, it might help when the background is cold or snow covered. Against a target above it, the sky is mostly cold with the exception of the sun, so it can track pretty well there too.
Radar seekers are another issue. In this case the signal is not coming from the target, but is the reflection of a signal from the launching aircraft (in most cases anyway). When the target is below the aircraft, its radar will hit the ground at some point, which scatters some of the signal back towards the launch aircraft. This results in a powerful signal that overwhelms the signal from the target. There is a lot of geometry involved; if the aircraft is directly below you then this is a problem, but if you are flying at, say, 30,000 and they are at 25,000, then they may still be above the horizon or close enough to it that your signal never returns (the horizon might be 500 miles away). Ground return was a significant problem with missiles like the Sparrow, which couldn't reliably be used against targets very far below the fighter.
Since the 1970s there have been a number of improvements that have largely eliminated this problem. One of the first was to use monopulse radars, which have additional coding in the signal, normally polarization, which allows it to filter out ground returns. When they were testing the Skyflash they could hit targets right on the ground, but had to keep the targets above 75m so their cameras could track them properly.
A more general solution is Doppler filtering, which lets you measure the relative speed of the returns, and filter out anything that has the speed of the ground as seen at that angle - the ground right below you isn't moving relative to you unless you're climbing or diving, but the ground in front of you is "moving" backward at whatever speed you're moving forward, and between those two the relative speed is changing based on the angle so its not entirely trivial. Well, at least until we had IC's, at which point it was trivial. Every modern radar missile I am aware of, and "modern" means "since the 1980s", uses this method.
As others have noted, it is also common for long-range missiles to climb to very high altitudes during the midcourse. This is known as a "lofted trajectory" or some variation on that theme. In addition to some of the ones mentioned above, the MBDA Meteor can do this, as well as any number of really long-range designs like the Seekbat, Eagle and R-37. Lofting is even more common in SAMs, where it is used by everything since the Nike Ajax - the Hercules used to go up to something like 120,000 feet before descending IIRC, and the Blue Envoy would have cruised at around 100,000 feet.

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text:
What are the meanings of these terms related to instrument flight?
Please describe and define the following terms:

Homing
0 degree relative bearing
Tracking
Hold
Entry
Holding pattern

What are its uses and purposes?

Any one to suggest a thorough instrument book as well.

Your book question may be covered here.

Consider the AIM (Airmans Information Manual) they exist online and cover most of these topics in clear written document form. I believe it's an FAA document infact.... also available in print form at your local airport FBO! -Brendan

The FAA'S Instrument Flying Handbook covers all those terms and more, but of course if you're not in the US then you should be careful to check that there no significant differences with the rules wherever you are

Homing & 0° relative bearing
Homing is a technique used with ADF/NDB navigation, where you point the ADF needle at 0° relative bearing, which means that your nose is directly pointed at the navigational aid you are trying to reach. The same technique can crudely be used with VORs and GPS, where homing onto a VOR would be changing the inbound radial every few minutes to establish a new heading to the VOR or using GPS GOTO every few minutes.
This is considered a poor navigational technique, as it purposely neglects wind correction and this the aircraft can get blown off track significantly. You also increase the leg time with this, as you take longer to reach the navaid than with wind correction applied.

(Image Source: navfltsim)
0° relative bearing refers to your longitudinal axis being in line with a navaid, mostly NDB. If something was straigh at your 3 o'clock, it would have a relative bearing of 90°, irrespective of your current magnetic heading.
Tracking
Tracking is technically the same as Homing, however wind correction is applied. Simplified, you account for wind direction and speed and correct your magnetic heading by the wind correction factor, giving you a new corrected heading, which allows you to track to the navaid you are trying to reach.

(Image Source: www.avstop.com)
Hold, Hold pattern and Hold entry
A hold or hold pattern is a racetrack defined by inbound course to a fix, a turn direction and turn time, usually given in minutes. A standard hold will usually be right turns with a timing of 4min for the racetrack, which is 1min for each 180° turn and 1min for each straight legs. Depending on from where you are trying to enter a hold, there will be different hold entry techniques.

(Image Source: www.americanflyers.net)

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text:
What is the front glass in fighter planes called?
What is the front glass in fighter planes called? I mean the one which had the reticle marked in them not the canopy glass. Cockpit part on google doesn't seem to tell what I want to know.
Are there any other uses of it besides targeting, because I have seen them only in fighter planes/jets?
When were they first employed?

I assume you mean the heads up display?

Please also make new questions from the second and third parts of your question- it helps keep content organized :)

If you are referring to the HUD, your last question is answered here.

It's a Head-Up Display, or HUD.

The HUD can display a number of different pieces of information, including performance data such as airspeed, altitude, and attitude, navigation data such as waypoints or ILS glideslope, or weapons data such as the selected weapon or the targeting reticle you mentioned. Thus, its uses are varied - depending on how sophisticated the system, basic aircraft control may be accomplished using only the HUD. In some modern fighters, there may be additional data on a Helmet Display (or in the case of the F-35, the helmet may have the only display).
It is not just used on fighters - some airliners, cargo planes, and trainers have HUDs:

(C-17)

(T-38)

(Airbus A380)
As for your last question, per fooot's comment, this question and answer has more information.

The Blackburn Buccaneer was the first production aircraft with a HUD and entered service in 1963.


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Why don't all wind tunnels use magnets to suspend models?
NASA and the French aerospace agency have conducted research into magnetic suspension and balancing systems (MSBS) to suspend models during wind tunnel tests, like this system in South Korea.

Where did the NASA and ONERA research lead?
If MSBS reduces interference from the springs and arms that usually hold models, why don't all wind tunnels use this technology? What are the disadvantages?

Also, can somebody create a wind-tunnel or wind-tunnel-testing tag?

Not too sure,  but I think magnets can't hold the models steady enough compared to springs and arms. Might also have to do with weight considerations.

Interesting concept! I would expect that controlling the strength and shape of the magnetic field must allow rapid changes, and historically such control was completely impossible. I would be interested to see the specs of the converters driving those magnets.

According to this SAE paper, "previous attempts at magnetic levitation within the aerospace community have been restricted to small scale due to the large magnetic air gap required between the model and the tunnel walls."

I think there are many reasons. First you cannot suspend any object with static magnets(There is a proved theorem for this) as it won't be stable. So complex electronics is needed. Magnetic force belongs on distance with square so very powerful magnets will be needed if model is not very close to the tunnel wall.

@PeterKämpf: Serious question, if we can (almost) land rockets back on earth, why can't we control the electromagnets of a magnetic wind tunnel?

@Andrius: I think you refer to Earnshaw's theorem.
Magnetism loses strength as $1/d^{3}$, but so what? If you use the tunnel at small scales, then I Think you can find strong enough magnets.

@Andrius Could you point us to the theorem? It would be possible as said, but the air gap would be a problem. Imagine you want to pipe water through a loop with two segments of pipe missing, most of the fluid gets lost. If you pay enough you could do it, you can even land a man on the moon. It's cool, but too expensive for regular use with current technlogy(even superconductor "floating), especially in big wind tunnells

Two reasons:

When a model is suspended in a magnetic field, and then the wind tunnel is switched on, you'll see a change in the force along 'y-axis' (The lift forces) and change in force along 'x-axis' (The drag forces). Hence, you'll need a complex mechanism for sensing this forces, and changing the magnetic field in such a way that the change in forces is compensated by the 'change in magnetic field' so that the model does not translate in any of these directions and stays static. Then you'd measure the change in magnetic field to measure the forces, and hence the system becomes expensive and cumbersome.
For pressure measurements, you'd have to use wireless sensors on the pitot ports, as you dont want tubes dangling form the suspended models. This makes the process more cumbersome and expensive

This is why the magnetic suspension is not used every where, as the cost to accuracy ratio in normal wind tunnels is much less than the ratio in magnetically suspended models of magnetic wind tunnels

Wouldn't the advantages of better model control during testing outweigh the initial expenses?
On a related note, what are the disadvantages of traditional wind tunnel setups?

@techSultan Who says the model control would be better? We have extremely good model control with the current mounts. Much better than with magnetic, I would guess, since it doesn't have to deal with the problem of the model moving when the wind stream changes. In particular, I would think that precise rotational control would be a pain with magnetic levitation, whereas it's easy with the current mechanical mounts. Also, we don't have to worry about the model flying off at Mach 2 and breaking stuff (or people) if (when) something goes wrong.

At least in the case of the U.S., almost all of our wind tunnels were build decades ago before the technology was available to do this. I used to work at the USAF base that has most of the US wind tunnels. Most of them are quite old. One of them was actually taken from NAZI Germany after the war, though I think that one is mothballed.
As far as the reasons they aren't widely used, these come to mind:

It's a lot more complicated to design and build. In engineering, you normally choose the less complicated solution if it's good enough. Apparently the existing ones are good enough because we've been using them quite effectively for several decades.
I'm sure it would require an enormous magnetic field, as those models can be quite large (several meters) and, thus, quite heavy. Given all of the very sensitive sensors in the tunnels, it would likely be a pain to keep the field from interfering with the rest of the electronics. This is especially true in the engine testing tunnels, since the engines themselves are full of electronics nowadays. Almost everything in modern jet engines is electronically controlled.

Hmm, I hadn't considered the magnetic interference in sensors. You say most wind tunnels were built decades ago. I assume that means no solid state electronics.
What if we built an MSBS-controlled wind tunnel with shielded wires and solid state electronics. Would magnetic interference still be an issue?

@techSultan I can't really speak to any specifics, especially since I can't remember how much of that stuff is classified, but I can't imagine that an enormous magnetic field in the test article area would be very helpful to the electronics.

It all goes back to classification. I guess I'll just ask my school's wind tunnel people. Thanks!


text:
Where can I find Delta flight schedule information in a structured format?
I downloaded Delta flight schedules from here but would like this information in a spreadsheet. Does something like that exist?

There are APIs to booking systems for this sort of thing to give you up-to-date information.

@MikeFoxtrot do you have a link for reference on such APIs ?

Have a look at this question from SO.


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Are strategic bombers still useful, or are fighters taking over this role?
During the mid 20th century and cold war, armies were having clear distinction between those aircraft designed as strategic bombers and those designed to be fighters for aerial combat. My understanding was that there were few exceptions to this rule.
However, the fifth generation of jet fighters include models designed normally for aerial combat but also used for strategic bombing. Old designs of strategic bombers are still being used, but it is clear that jet aircraft are being significantly improved by new developments compared to obsolete bombers.
Why is this happening? Is current warfare no longer requiring strategic bombers? Are designs of jet fighters so flexible that they can perform different missions? (usually it is the other way around, as time passes more specialization is seen).

The age of bombers is discussed here and the usefulness discussed here.

@fooot um... interesting articles, both are addressing part of the question but not all. Part of my question is understand why newer jet fighters are used for typical strategic bombers missiong, which is agaisnt what is described there, as strategic bombers are more cost effecive following one of the discussions.

That is a very involved question studied at the highest levels in air forces around the world. The bomber's problem is that it is, in many ways, a very specialized instrument and, in absolute terms, very expensive to own and operate; to say nothing of its decreasing survivability on the modern battlefield. Tactical aircraft, by comparison, have become exponentially more lethal due to new mission electronics and smart munitions. For countries without the resources or need to deploy strategic bombers (which is most of them), tactical is much more practical, scaleable and sustainable solution.

Seems to me that, given the current & foreseeable state of geopolitics, the real question ought to be whether there's a real role for actual fighter aircraft, in the air-air combat sense.

I would argue that most fighters have features that allow them to accomplish tactical bombing, not strategic.

The reason that small aircraft are used in the bombing role is flexibility and cost. If you load up a B-52, it can only be in one place at one time, travel at subsonic speeds, and be expensive to operate, risking more crew and equipment. Using smaller attack jets allows reaching targets across a wider geographical area faster. And while past conflicts saw massive bombing campaigns that favored the use of large bombers, more recent conflicts have seen much less of this tactic. Smaller, more targeted strikes are more typical, where a large bomber would be overkill.
Take a look at the cost per flight hour for various aircraft. A B-52 will cost \$70,000 per hour to operate, and a B-1B \$60,000. Compare this to an F-16C for \$23,000 or an F-15C for \$42,000. The A-10 costs \$18,000. For stealth, the costs go up to \$170,000 for a B-2 and \$70,000 for an F-22. So why send a B-52, when a few F-16's would cost the same amount? The fighters will also be able to defend themselves, and still be able to carry out a mission if an aircraft drops out. The same argument can be made for the stealthy class.
Strategic bombers still have their uses, but the bomber role is much less demanding than the fighter role. With proper maintenance and multiple equipment upgrades, old bombers can still fly bombs to their targets just fine. Fighter jets have much more complicated requirements, such as stealth, speed, and maneuverability, where advances in technology will justify the costs of continued development of new designs.
Aircraft are becoming more generalized because it is more efficient. In some areas such as naval aviation, this is even more critical. Why have separate planes for electronic warfare, attack, and air defense? You would be limited to a certain number of each type, with little or no cross capability. But with more generalized aircraft, you can have more aircraft with a certain capability across the fleet. If a certain capability becomes less important, you don't end up with a whole group of aircraft becoming useless. Aircraft can fulfill multiple roles in a single mission or deployment.

So a B-1B can carry seven times as much ordnance as an F-16, at less than three times the cost per hour. Score one for the strategic bomber. Ten times the combat radius, too. (Source: Wikipedia, B-1B, F-16C.)

There are very few mission profiles in modern (post-WWII) combat that call for "carpet-bombing" of the type that the WWII-era medium and heavy bombers were used for. The primary target of a strategic bombing campaign is typically a city or other highly-populated area. During WWII it was considered a necessary evil, as high-value military-industrial targets were typically located in these cities and the accuracy (and power) of bombs was sharply limited, usually requiring an entire wing of bombers to ensure complete destruction of the target. This approach has since has been eschewed as barbaric by nations with significant air forces.
Technologically, advances have continued to chip away at the heavy bomber's mission profile. Small, precision bombing campaigns have always been given to light bombers like the Stuka, Mosquito and Mitchell, and in later eras the F-100 Super Sabre, F-105 Thunderchief (aka the Thud), A-6 Intruder and A-7 Corsair. These later aircraft used the development of the electronic fire control computer to dramatically increase the precision of unguided weapons, which along with their greater speed against enemy interceptor aircraft rendered the familiar sight of a sky darkened with large bombers unnecessary. In modern warfare, there are few dedicated small ground attack aircraft (the A-10 being a notable exception designed for close air support), most of that going to "multirole" aircraft such as the F-16 and F/A-18, with a few "deep strike" fighters like the F-15E (and when a similar mission profile but more firepower is called for, the B-1B finds its niche). These fighters handle the majority of offensive operations against high-value targets and enemy air defenses ("Wild Weasel" missions), with the A-10, AC-130 and Army helicopters handling the direct threats to infantry and armor.
In the early Cold War era, the best and biggest reason to keep heavy bombers like the B-29, B-48 and B-52 was that they were the only suitable vehicle for the delivery of strategic nuclear weapons (>1Mt). These weapons were phased out of the U.S. arsenal with the introduction of the MIRV-capable ICBM, able to carry the same total payload much farther, faster and with less impact of attrition by defenses, and shortly afte the dissolution of the Soviet Union, the Strategic Air Command itself, the single largest operating authority of the B-52 in history, was dissolved.
The last big reason to have something like a B-52 in theater is the ability to loiter indefinitely (at least 24 hours at a stretch). B-52s have the size and crew space to allow for crew rotations (you're not going to find Stearns and Foster mattresses aboard, but there are a few places to stretch out and kip, and there is a crude lavatory known sarcastically as a "honey bucket"), and with in-flight refueling, the only serious limitations to flight time are the capacity for on-board food stores and the eventual depletion of munitions. The B-52 can be equipped with 336 GPS-guided JDAM weapons, and a B-52 loitering at 50,000 feet over a theater like Afghanistan can be directed via AWACS/JSTARS to drop a guided bomb at a target with no visual line-of-sight needed. If air defenses are a potential problem, it has far-BVR capabilities when using cruise missiles like the JSOW, though it can carry fewer of them. This is the B-52's last stronghold, and it's a significant one; given various upgrades for efficiency and technological improvement during its life, the USAF plans to maintain a modest number of these aircraft until at least 2040.

Good catch with loiter time. That is something people have been complaining about regarding the retirement of A10. The F-series and drones do a strike and go away and some threats do not respond well to that model. Like infantry taking cover in urban areas or other terrain with lots of cover. You really want air support that can stay over and keep supporting until it is no longer needed for that. If A10 gets retired B52 is pretty much only thing that can do it. Although dropping bombs doesn't really replace autocannon, if friendly troops are nearby...

@VilleNiemi: B-52 can't really do close air support. AC-130 is the thing for that.

@JanHudec True, which is why it can't replace A10 meaningfully, but it fills the same gap in the capabilities of the general purpose fighters. For some reason when I have a character limit, my comments become pretty misleading...

I'm an A-10 fan myself, and yes, loiter capability is a big reason they're still around. AFAIK, though, the CAS role is being given more and more to Army helicopters. The A-10 first flew 2 years after the introduction of the Apache and the Hellfire missile, which gave the Army the airborne anti-tank weapon that was lacking in the Cobra and Huey, and the Air Force top brass (and many pilots) were content to let the Army handle its own CAS at the time. The A-10 eventually proved its worth, and a squadron of them are now getting it done against ISIS.

Fighter aircraft have steadily grown in size and mass over the last century, as performance requirements and their armament load spiraled upwards. This has reached a point where a single seater today will carry more ordnance and fly farther than a strategic bomber from 70 years ago.
With their size and performance, the price of a single aircraft went through the roof, such that now one single aircraft design must fulfill many roles where 70 years ago several companies could offer competing designs for specialized roles. The development of strategic bombers has effectively stopped several decades ago with the XB-70, the B-1 and the Tu-160 because it became unaffordable. Note that I did not mention the B-2: It must be judged an economic failure, being so expensive that it rarely is used in earnest for fear of losing just a single plane. Instead, bombing missions today are performed by the smallest and lightest front line fighters, because here single-digit losses can still be tolerated.
Even attempts to break this spiral (the Folland Gnat or the Northrop F-5 come to mind) went nowhere. Note that both types were not accepted in their intended role by their respective nations, but could only serve in their training variants.
Today we keep old designs up to date by updating systems, but in many cases the airframe flew first before today's pilots were born. Engineers will rarely work on more than one new frontline combat aircraft design in their whole lifetime because development cycles now stretch over three decades. Compare that to the situation in WWI, when aircraft designs normally became obsolete within one year of their introduction.
Strategic bombing is also no longer part of military doctrine. Instead, the goal is to limit escalation and use highly precise strikes against selected targets. Compare that with the situation in WWII, when the declared goal of bombing was to wear enemy morale down and kill as many people as possible. Back then, collateral damage was a desired side effect, whereas it has become indefensible today. Let's not forget that one of the first (relatively) long-range bombing missions in history targeted a matinée circus performance in Karlsruhe, when heroic French pilots managed to take 120 lives, mostly children and their nannies, on an afternoon raid in June 1916.
To be blunt, classical strategic bombing is as dead as the parrot in that Monty Python sketch.

The size / weight argument is pretty compelling. A World War II B-17G (MTOW 65,500 lb / 24,500 kg) strategic bomber is significantly lighter than an F-22A (MTOW 83,500 lb / 38,000 kg) air superiority fighter, though the F-22 is one of the heaviest fighters currently in operation worldwide.

I think the bombing mission in WWI during which a circus was hit happened in Karlsruhe, not Freiburg.

The platform dropping the bombs becomes less and less important every year.  GPS guided bombs can strike a target with the same precision employed from any aircraft flying at 30,000 feet or above.  So the type of aircraft doesn't matter much, and it matters less and less as time passes.
The aircraft has simply become a mule to get the bombs to the airspace above the target.  Being a dumb mule is a perfect role for an unmanned aircraft, so expect more drones to take over the bombing roles in future decades.  Unmanned aircraft will replace both fighters and strategic bombers in the bomber role.


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What are the limitations in adoptions of GTF (Geared Turbofan) technology?
The only recent engine using GTF technology is the PW1000G, however some old designs like ALF502 or TFE731 use this technology. I understand the basic concept of the benefit obtained by the engine introducing this technology (basically giving another parameter to optimize RPMs at low pressure turbine and fan) and that benefit is compensated by the increase in weight.
What is blocking this technology to be further included in modern turbofans? Is it only a business case for P&W architecture?
What made it possible in PW1000G that blocked PW8000?

The TFR731 is 3500 lb thrust, and the ALF502 is 7000 lb thrust. The PW1000G is in the 20,000 lb thrust class. This is a big difference.

Could you develop that argument further, finally I guess that the key question is the ratio between both optimum RPMs, how that changes with the size (in terms of thrust) of the engine?

Nobody wants to risk putting 50,000 hp through some groovy wheels?

The factors that are relevant here are:

Increasing the bypass ratio is very desirable in order to improve the efficiency of the engine, and for the same amount of thrust, this means increasing the fan diameter.
In order to keep the fan mostly subsonic, the fan rotational speed has to decrease with increasing fan diameters. Supersonic fan blade tips are possible and in use, but you lose efficiency and increase noise, so it's desirable to limit this to the outermost area.
For the same efficiency, a low-speed turbine requires more stages and therefore more weight compared to a high-speed turbine. Compare the PW1100G's 3-stage LPT (geared) with LEAP-1A's 7-stage LPT (not geared).
The only way to decouple the rotational speed of the LPT from the rotational speed of the fan is by using a gearbox.

In the long run, this is therefore a question of whether the gearbox is heavier than a slower-turning LPT and whether a possible increase in maintenance costs due to the gearbox is acceptable for the given gain in efficiency or reduction in engine weight. With further increases in engine bypass ratios, the gearbox becomes increasingly attractive.
In the short run, this is also a question of whether a company wants to risk developing a completely new component, with potential problems before and after entry into service. Additionally, with a given amount of money and manpower to develop a new engine, management will ask: Where are the engineering hours going to make a bigger difference, in improved fan, compressor, turbine and combution chamber designs/materials/... or in a gearbox design.
So while, for example, Rolls-Royce does not manufacture a geared turbofan right now, their "UltraFan" research engine project does include a gearbox. I think it's safe to say that it is only a matter of time until most commercial turbofans will include a gearbox.

I think this is the answer I was looking for. Quick question, why slow moving turbines require more stages? Is because energy transfer is proportional to the square of the rpms?

Assuming an Euler turbine, the energy transfer in one rotor stage is: P = mp * u * dwu, where mp is the mass flow, u is the rotor speed and dwu is the difference in radial flow speed of the fluid before and after the rotor, i.e. the amount by which the fluid "changed direction". Since dwu is usually in the proximity of u, for a given mass flow and axial speed, I would agree that your statement is approximately correct. Corrections are welcome.

In completion to @JulianHzg's anwser:

Increasing the bypass ratio is very desirable in order to improve the efficiency of the engine, and for the same amount of thrust, this means increasing the fan diameter

Increasing the bypass ratio is surely a way to reach a higher efficiency (and maybe the most developed topic at the moment in aircraft engines), but only if you can provide the engine with a powerful enough gas generator, so increasing the bypass ratio is constrained by other parameters such as combustion chamber temperature and turbine efficiency.

In order to keep the fan mostly subsonic, the fan rotational speed has to decrease with increasing fan diameters. Supersonic fan blade tips are possible and in use, but you lose efficiency and increase noise, so it's desirable to limit this to the outermost area.

Also, blades permanently submitted to shock waves tend to have a very short lifespan because of very high cycle fatigue. Therefore, people tend to avoid supersonic flow conditions.

For the same efficiency, a low-speed turbine requires more stages and therefore more weight compared to a high-speed turbine. Compare the PW1100G's 3-stage LPT (geared) with LEAP-1A's 7-stage LPT (not geared).

Basically, the rotational speed of every element must be adapted to the fluid velocity. So if every rotating element is driven by the same shaft, the flow must be adapted adding stages in the turbine or compressor modules. If you have two shafts, one slow (good for the fan) and one fast (good for the turbine) you get a better compromise in terms of efficiency. However, this poses other issues (rotordynamic instabilities for instance) which explains why Rolls-Royce is the only manufacturer to propose three shafts (even better in terms of efficiency but also very complex).
The gearbox allows to keep using two shafts while improving adaptation between fluid and rotating element.
The question about the weight of the gearbox is very important, is must be recalled that a gearbox mut be able to transmit the power of the LPT to the fan, so it's not a simple gearbox from your car. Also, although epicycloïdal gearboxes have a very good efficieny transmitting power using such trains costs energy, creates heat, requires lubrication and maintenance.
To conclude, this is a very well know technology that is even well known to the aeronautic industry (how do you think helicopters fly !), but that was never used on high-power aircraft engines. Another application of gearboxes are the open-rotor engines which involve even more complex transmissions du to counter rotating fans.

You say that "blades permanently submitted to shock waves tend to have a very short lifespan because of very high cycle fatigue". This would be caused by oscillating shocks - is that really common on fan blades? As long as the shock location stays reasonably fixed, there should be no fatigue issues from supersonic operation.

@PeterKämpf, I agree that if the schocks location is fixed, there should be no HCF. I am just wondering about the problems brought by the coupling of other phenomena with schock waves, especially flutter, which lead to HCF


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Is there a formula to calculate ground distance traveled given rate of climb and true airspeed?
I'm looking for a formula to calculate the horizontal distance (guess it is the Ground Distance) passed during the phase of ascent (or descent), having the rate of climb in ft/min and the TAS in knots. I did not found a clear answer about this question. I think it may concern with the Climb Gradient.
Refering to the image below, I'm trying to calculate d, having:

h = 11200 ft
RoC = 1250 ft/min
TAS = 75 kn

ClimbGradient = (RoC / TAS) * 6000 / 6076,12 = (1250 / 75) * 0.9874 = 16.45%
d = h / (ClimbGradient * 100) = 11200 / 1645.78711 = 6.80525 nm

Is this correct calculation? I will update this question with the correct formula in other case.

Air speed does not relate to ground speed so you can't determine the distance covered over the ground. Think about if the aircraft has a very strong headwind, it will be travelling slower over the ground vs an aircraft with a strong tailwind. The rate of descent gives a time, and true air speed gives speed through the air, but not over the ground.

@Ron Beyer is correct, but another significant factor is that winds vary through altitudes.  Although they are generally higher at higher altitudes, the wind direction will normally vary also.  Therefore, for a reliable figure, you need winds aloft profiles through the climb corridor.

@Yohji please specify if the calculation takes place at zero wind.

@Koyovis the discussed formula take place in still air, and it would be an approximation by this way.

The first bit of your computation is correct: 16.45% = 0.1645. Then if you would divide 11,200 feet by 0.1645 you would get pretty close to 11 nm.

If you assume no wind, the problem is a simple trigonometry problem.  If there is a wind but you don't know what it is, you'll end up with an equation, not a numerical answer.

Pythagoras has your answer.
You've been climbing for 11200/1250 = 8.96 minutes
In that time you've traveled 75 * 8.96/60 = 11.2 nautical miles = 68,051 ft along the diagonal D
$D^2$ = $d^2$ + $h^2$ => d = 67,123 ft = 11.05 nm

You've travelled that distance through the air not over the ground.

You've travelled 11.2 nm through the air.

Right, but what if I told you that if you had a strong enough headwind, you could make that climb in 2 miles of ground distance? The question asks about the distance over the ground traveled in the climb, not the distance in the air.

I'm assuming the question would be at zero wind. It would lack an input otherwise.

I'm was thinking too about the Pythagorean theorem. The question is about the distance travelled over the ground (the d in the picture), as if the plane for absurdity never takeoff.

Yes. D = 11.2 and d = 11.05. They are very close because the angle is only 9.6º

.there is no requirement for long formula, if you know the ground speed, then you can  calculate the climb horizontal distance, if GS is  75kt
climb distance = GS* climbing time
Climbing time = 11200/1250
               =  8.96min
Climbing distance = 8.96* 75/60 = 11.2 nm


text:
What's the reason for pilots wearing uniforms?
Just came across an interesting answer to a question on uniforms for PPL Human Performance and Limitations:

Pilots wear uniforms:
a) so they can be easily recognised
b) so that they can be perceived to be important
c) so that they can feel important

Apparently the correct answer is b (I said a). Is this so that their authority is respected, is this a valid reason?

Can you imagine a pilot walking into an airplane in his sweat suit? I bet we would all run away from there. This same logic applies to other jobs where responsibility relies on a few number of people. So yeah, how others perceive you is key here. Don't forget that a pilot is the authority on an aircraft.

PPL = Private Pilot's License?  I can't understand why such a question would be asked there.  As a private pilot, I can assure you that I've never worn a uniform, and quite often do fly in sweats :-)  For commercial pilots, I expect the answer is "Because the employer requires it as a condition of employment."

@jamesqf As a former airline pilot (retired 1999), I agree that for many the reason they wore the uniform was because it was a condition of employment. That was certainly true for me, personally. However, some, what percentage I can't say, needed it for their ego or some other reason not really related to the performance of the job. FWIW, I once flew a heat-soaked 747 freighter with an inop APU in running shoes and running shorts, as did my f.o. and f.e. on that occasion.

I, too, would have answered (a) as the best answer. Further I would argue that (b) is not a better answer as it's written. To me, "importance" smacks more of celebrity as in V.I.P. rather than competence and command.

YouTube channel Mentour has a good video on this subject.
He says Pan Am introduced the Navy style uniforms to pilots in the 30's when they operated flying boats to calm the passengers down.

Airline pilot uniforms started being used by Pan Am in the 1930s to make the pilots look more professional and experienced which would calm nervous fliers down.  If you don't understand, just imagine someone saying "Hey, that pilot looks elegant and professional!  He sure knows what he's doing."  This is why most airlines require pilots to cover up their tattoos, etc.  Pilots are also required to take good care of their uniforms for the same reason.

Do you happen to have sources for your statements?

https://en.wikipedia.org/wiki/Airline_pilot_uniforms, https://www.youtube.com/watch?v=HOB7noUGsF8, and personal knowledge if that counts.


text:
What responsibility does a pilot have for people on the ground when making an emergency landing?
Recently, a Cessna made an emergency landing on a crowded beach in Portugal. The two occupants of the aircraft did not sustain any serious injuries, but two people on the ground died.
A couple of years ago, a similar incident occurred with a Piper in Florida. Again, the occupants were unharmed, while two people on the ground died — one at the scene, the other later succumbed to her injuries. The main difference is that here, the pilot hadn't noticed them and thought he was landing on an empty beach.
In Portugal, however, the beach was not just not empty, it was crowded. And the pilot could have known it would be, too — it was summer in Europe and a lot of beaches are crowded every summer.
It's hard to tell while the investigation is still ongoing, but in a situation like this, shouldn't a pilot choose another way to resolve the emergency?
I understand that a pilot's first responsibility is to the people on board the aircraft, but what are a pilot's responsibilities to people on the ground?
Are there any differences in the different legislations (FAA / EASA)?
Are there any other laws applicable? Have any precedents been set in court?

As noted in a comment, the flight instructor and the trainee have appeared in court, facing charges of negligent homicide.
"Portugal pair in court after fatal plane beach crash", BBC News.

I think we should restrict this to a legislation, EASA/EU/Portugal laws might be different from FFA/US ones

@Federico perhaps, but does the EU legislation differ that much from the US?

I don't know, but to prevent N different answers all about different legislatures, it's upon you to decide which legislature you are interested in and to clarify that with the appropriate tag.

@Federico Actually, I'm interested in learning about those differences if they do exist; a good answer should address these.

note that if you make the question too much about this specific case, it can get closed as opinion-based (you are asking us to evaluate something that is currently in court, an we are not the court). I suggest you to keep it eventually based on the fact, but a general question.

Factors in pilot choices are often subject to political spins, as few people are able to objectively evaluate the information available to the pilot, the bandwidth to manage the events, and the conditions which may have added complexity as well as the experience level of the pilot. A student pilot logically is held to a different competency expectation than a commercial/ATP with 15,000 hours in type, intimately familiar with the conditions, etc.
In common law, the pilot is supposed to protect in order, innocent third parties, the passengers, the crew, and property of others.
Where there were people impacted (no pun intended) who were not seen or known to the pilot/crew, that becomes a mitigating factor.
The bulk of civil liabilities on flight crews is established in case law, as there are few statutes which address that, at least in the US and Canada.
Addendum #1 Protection of innocent third parties, is first order as they have not elected to become part of an aviation event.  Passengers need protection because it is the duty of the crew to protect passengers, even if non-paying. Of course passengers assumed some risk by electing to fly. Crew need protection because they are humans.  Property is last.
Addendum #2, incorporation of comments, per requests. Comments are largely unedited, simply included to preserve the record. The comments were in response to a challenge for authorities on the common law obligations of pilots.
HLS Torts 2, Aviation under the Common Law, Francis H. Bohlen , and for contributory relation: Recreational boating accidents: Which law applies? Kevin Donius, for duties: TRITCH, ALLAN M. University of St. Thomas Law Journal: Fides et lustitia 2014/04/01, Vol: 11, p331, for practicality, and legislative mix: Fifty Years of Torts Harvard Law Review, Vol. 50, No. 5, Kohr, 504 F.2d 400 (creating federal common law of contribution in aviation accident). Kohr figures prominently in Professor Field's theory of federal common law, see Field, supra note 14, at 913-15, but almost certainly does not survive the refusal to create a federal common law right of contribution in antitrust cases. Tex. Indus., Inc. v. Radcliff Materials, Inc., 451 U.S. 630 (1981)
But see Musick, Peeler & Garrett v. Employers Ins. of Wausau, 508 U.S. 286, 292 (1993) (creating "ancillary" common law right of contribution in implied Rule 10b-5 right of action). Indeed, within seven years of Kohr, even the Seventh Circuit did not think to use federal common law to deal with the complex conundrums of choice of law analysis in an aviation accident. In re Air Crash Disaster Near Chicago, Ill. on May 25, 1979, 644 F.2d 594 (7th Cir. 1981).
The Bohlen one, while dated (~1937) hits many of the foundations. But the boating one points out that by being a passenger you accept a greater risk than an independent third party. In the Torts class, I did a couple of papers on aviation torts. The rest of the cites become rather obtuse, because the focus in most litigation is not on common law, but on statutes. Yet, in NY, the bar exam covers common law. Go figure.
I cannot comment of EASA regulations, but generally the FAA regulations do not cover tort liabilities. Tort law and common law, where applicable, would appropriate references. This may be more relevant for SE Law. FAA regulations cover operational matters, certification, registration and administrative aspects of aviation.
Also the liabilities can be quite complex, for example in the Chicago crash, state Public Utilities Act was invoked, which added one of many local complexities to the litigation. That kind is stuff is, I believe, beyond the scope of SE Aviation.
This congressional intent not to exclude state statutory and common law from the field of aircraft safety is further illustrated by the existence within the Federal Aviation Act of a savings clause. 49 U.S.C. app. 1506 (1988)

"In common law, the pilot is supposed to protect in order, innocent third parties, the passengers, the crew, and property of others." Do you have any sources for that?

HLS Torts 2,  Aviation under the Common Law,
Francis H. Bohlen , and for contributory relation:  Recreational boating accidents: Which law applies? Kevin Donius, for duties: TRITCH, ALLAN M. University of St. Thomas Law Journal: Fides et lustitia 2014/04/01, Vol: 11, p331, for practicality, and legislative mix: Fifty Years of Torts Harvard Law Review, Vol. 50, No. 5,

Kohr, 504 F.2d 400 (creating federal common law of contribution in aviation accident). Kohr figures prominently in Professor Field's theory of federal common law, see Field, supra note 14, at 913-15, but almost certainly does not survive the refusal to create a federal common law right of contribution in antitrust cases. Tex. Indus., Inc. v. Radcliff Materials, Inc., 451 U.S. 630 (1981).

But see Musick, Peeler & Garrett v. Employers Ins. of Wausau, 508 U.S. 286, 292 (1993) (creating "ancillary" common law right of contribution in implied Rule 10b-5 right of action). Indeed, within seven years of Kohr, even the Seventh Circuit did not think to use federal common law to deal with the complex conundrums of choice of law analysis in an aviation accident. In re Air Crash Disaster Near Chicago, Ill. on May 25, 1979, 644 F.2d 594 (7th Cir. 1981).

+1, the most impressive citation this site has ever seen. It puts the citations in law.se to shame

Thank you, but you might reserve the compliment until reading all of them.  The Bohlen one, while dated (~1937) hits many of the foundations. But the boating one points out that by being a passenger you accept a greater risk than an independent third party.  In the Torts class, I did a couple of papers on aviation torts. The rest of the cites become rather obtuse, because the focus in most litigation is not on common law, but on statutes.  Yet, in NY, the bar exam covers common law. Go figure.

I cannot comment of EASA regulations, but generally the FAA regulations do not cover tort liabilities.  Tort law and common law, where applicable, would appropriate references.  This may be more relevant for SE Law.  FAA regulations cover operational matters, certification, registration and administrative aspects of aviation.

Also the liabilities can be quite complex, for example in the Chicago crash, state Public Utilities Act was invoked, which added one of many local complexities to the litigation. That kind is stuff is, I believe, beyond the scope of SE Aviation.

This congressional intent not to exclude state statutory and common law from the field of aircraft safety is further illustrated by the existence within the Federal Aviation Act of a savings clause. 49 U.S.C. app. 1506 (1988)


text:
To what extent is remuneration under a PPL enforced in the UK?
I came across this, How do PPL, CPL, and ATPL compare? and was intrigued by the fact that a PPL cannot fly for any payment whatsoever.
To what extent is this enforced?  An example scenario would suggest that, for example, I fly my employer to an exhibition on the continent, which he then claims from the company and privately reimburses me for the hire and landing fees. Alternatively, I receive some kind of company bonus to cover the cost, or even further, he blatantly pays on a company card.
Is this illegal? How could this kind of activity be stopped?

Welcome to Aviation.SE. Firstly, don't try to bend definition of payment. Payment is payment regardless of the form it comes in. Second, even if a rule isn't enforced, doesn't make it right.

I wasn't trying to bend anything or suggest future intentions here, and I certainly don't like breaking laws. I was just giving the first example that came to mind, and to stimulate a discussion about this topic, which clearly must be broken on a regular basis. I do believe the question was, how is this enforced?

Welcome to aviation.SE! This is an interesting question and I hope you get a good answer, but please note that this isn't a forum: the goal of all SE sites is not to discuss topics but rather to give the best possible answer to a specific question. You might want to check out the [tour] if you haven't already, to get some more background on how the site works.

Yes it's illegal.  How can it be enforced?  Like any other law.

So why would authorities such as the CAA create laws like this if there was no way of enforcing it? I came across some official documentation on the CAA's website, saying that of August 2016, flights can be 'cost-shared' by up to a maximum of 6 people, across the EU. This seems to me that this remuneration law is only applicable to scenarios which include making profit, such as pleasure flights. https://www.caa.co.uk/General-aviation/Aircraft-ownership-and-maintenance/Guidance-on-cost-sharing-and-introductory-flights/

You can cost share providing that the cost is split exactly equally i.e. you must not profit from it.  It can be enforced, as I say like any other law, and there have been successful prosecutions.

The comments and only answer (so far) show you that this is not the appropriate place to ask about legality. You should consult a solicitor, not random people on the internet. The CAA website has plenty of references to enforcement of the ANO and how it uses its powers.

Flying your boss to any function related to work is a commercial flight under most jurisdictions, and cannot be done using a PPL regardless whether you're paid or not.

The rules are as follows:

Privileges and limitations

A holder of a PPL may, for compensation or hire, act as a crewmember of an aircraft in connection with any business or
  employment if—

a. the flight is only incidental to that business or employment; and
  b. the aircraft does not carry passengers or property for compensation
  or hire.

"Compensation or hire" means income, not expenses. You can always be reimbursed for expenses such as fuels. Only income is forbidden under certain circumstances (see below).
Concerning getting income, you can be paid income if both of conditions (a) and (b) above true. That means your business cannot be anything to do with flight. If your company is Boeing or any air-travel related business, you cannot receive ANY income (even your salary) for piloting such a flight.
The aircraft cannot be used to carry paying passengers or cargo.
So, basically what this means is that if you fly anybody from your company, they can pay only the expenses of the aircraft and nothing else. You can be paid your salary, only if flying is not your job in any way. As long as you have a regular job and it is fully incidental to flying, then you can fly clients and fellow employees and receive expense reimbursement only. If you are flying clients, they cannot in any way be paying money for the flight other than direct expenses like fuel.
The usual consequence of violating these regulations is that your license to fly can be suspended or revoked. Technically speaking, flying for hire without a license is a minor criminal offense (see below), however prosecutions in the past have only been given out for egregious violations (like working for a charter company without a commercial license).
The way these regulations are enforced is the following:
(1) If you are flying passengers or cargo for hire, and somebody rats you out, complains to the CAA, or it otherwise comes to their attention, then they will investigate and revoke your license if they determine you are flying for hire.
(2) The CAA has inspectors and they may do surprise inspections of aircraft. If you start flying passengers regularly, you may get inspected. If the inspector finds you are flying a bunch of passengers with a PPL, they will closely question your passengers about what money those people are paying. If the inspector determines they are paying money other than incidental expenses to be flown, you will likely have your PPL license revoked.
EXAMPLE:
You are flying 3 colleagues to a business meeting. A CAA inspector directs you to park on the ramp and inspects you and finds out you have a PPL. He will then question your passengers. How much are you paying for this flight? Colleagues answer:
(1) "nothing". You are ok.
(2) "18 pounds". You are probably ok.
(3) "200 pounds". You will lose your license.
If he see cargo on the aircraft, then there are two possibilities:
(1) He determines that the cargo is incidental to the flight and it belongs to you. (Like scientific equipment and you are a professor flying to an archeological site). You are ok.
(4) He sees cargo on the aircraft that does NOT belong to you (like 8 cases of computer chips being delivered to an electronics company). You will lose your license because you are flying cargo for hire.
Criminal Issues
Note that technically, flying for hire is a minor criminal offense in the UK and can be punished with a fine up to 2500 pounds in a magistrate court. However, it is very rare for this kind of offense to be criminally prosecuted. In the linked news story it was found there was only a single prosecution over the course of a year, and in that case it was a pilot working for a charter company and doing many commercial passenger flights, which was a blatant violation of the rules.

The CAA has civil and criminal powers to bring prosecutions.  They can do far more than invoke your license.

@Simon According to my reading, Section 40 is a civil regulation. The worst penalty is license revocation. If you have evidence to the contrary, cite it.

You could start here. https://www.caa.co.uk/Data-and-analysis/Data-for-passengers/Complaints-and-enforcement/Enforcement-actions/.  The regulatory environment is very different to the US.  The Air Navigation Order is a statutory instrument and is part of the Civil Aviation Act.  The CAA has power to bring either civil or criminal prosecutions for violations.   https://www.caa.co.uk/uploadedFiles/CAA/Content/Standard_Content/Data_and_analysis/Datasets/Prosecutions/CAA%20prosecution%20results%202005-06.pdf.  You should be careful in suggesting that revocation of license is the worst penalty.

@Simon I researched it and apparently a licensing violation qualifies for a Schedule A penalty which is a maximum 2500 pound fine in a magistrate court, so I guess that would be the equivalent of a misdemeanor in the US. However, I would suspect the CAA would only refer someone to criminal prosecution for a hire violation if it was a pretty egregious case. However, not being a UK citizen I don't know how the CAA behaves. I did some research on this question and have updated my answer with the results.

May I suggest that you edit your post to remove the statement that they are "just rules"?  A criminal conviction, whether in a magistrates court or a high court is a very serious blemish.  It is, for example, enough to get you refused entry into many countries, including the US.

@Simon Yes, I made that change, since as you pointed out, the license requirements do apparently have the force of law in the UK.

@Tyler Durden Thankyou, This answers my question perfectly. So e.g. it costs 200 to hire the plane and land it at another airfield, and that is all that I am paid, that is legal, but if I charged over that, then that is effectively illegal unless it fits both condition a) and b)?

@E.Nunn If you rent the plane, theoretically you could expense that cost. So, for example, if the rental costs 200 pounds and you were flying 3 others, you would split it 4 ways, each paying 50 pounds. Keep all receipts. If you pay an equal share, it is evidence that you are not receiving compensation, so it is always a good idea to do that.

@E.Nunn No.  If it costs £200, you must pay an equal share with all other passengers.  You cannot "charge" or be "paid" for anything.

Simon and Tyler, Ah right. I was getting a little mixed up. My reasoning was that I initially paid for the flight/rental and then the other passengers reimbursed to the total expense and not further. Thank you both for confirming that this statement is not correct!

Never realized the uk rules were so much more liberal on payment. If your passenger so much as says "Thank you" the FAA considers it compensation!

There are some long answers to a simple question here. In the UK private pilot license holders are allowed to share the direct costs of a flight between a maximum of 6 people including the pilot although how much the pilot has to contribute isn’t specified. Direct costs are things like, fuel, aircraft hire and landing fees.

Welcome! That's true but the question is not what are the rules, but how much they are enforced.


text:
In the context of aircraft design, what are the differences between a flat plate shaped airfoil and a droplet shaped airfoil?
I am relatively new to aerodynamics and am curious to know what difference it makes on an aircraft - lift, drag, weight etc - which of the two airfoils is used on the wing.

i think this will get dupe'd but since someone asked, i'll answer

related (if not a dupe): How do paper airplanes create lift if their wings are flat?. Both questions have different approaches (and I think both should be kept on this website) but leads to the same topic: the difference between a flat airfoil and a more usual shape.

Re "What is the difference between a flat plate shaped airfoil and a droplet shaped airfoil?" -- one difference is that one is shaped like a flat plate and the other is shaped like a droplet.  If you are interested in asking about other differences (like the lift coefficient acheived at a given angle-of-attack?) you might consider editing the title to reflect that.  Also please include your question in the body of the post, not in the title only.

I get the impression he's asking "why do we not use flat plate wings"

What was the downvote for?

The droplet shaped airfoil has multiple advantages.

It provides space for storing stiffening structures. The flat plate foil is very thin, so would need to be quite heavy to maintain stiffness, as stiffness is proportional to the square of the thickness.
It provides space for storing fuel. This is important to reduce weight on modern cantilever aircraft. Distributing weight along the wings reduces the bending caused by the heavy fuselage during flight. On the ground, the extra weight (and bending) from the fuel is little, since the fuel is not as heavy as the fuselage!
It provides good performance across a range of angles of attack. (Angle of attack is the difference between the direction of motion and the direction you're facing.) The round leading edge allows air to smoothly flow over it when this angle is high, for example during climb or slow flight.
It gives gentle stalls. (A stall is when increasing the angle of attack does not increase lift force anymore, and instead decreases it.)

Flat plate wings will stall suddenly and violently as soon as the angle of attack needed to stall is reached, as the flow separates across the whole wing at once. (Flow separation is when a region of air moving in reverse develops on the wing, causing the airflow on the wing to flow around this region, which creates less lift and more drag.)
But the greater curvature on the top of the teardrop foil causes flow separation to happen at the rear of the wing first, as angle of attack continues to approach the value needed for stall, warning the pilot that any further increase will stall the plane.
But for supersonic applications, the teardrop foil does not work very well. At these speeds, the extra drag from the bluntness begins to outweigh any other benefit. So, an thin, sharp foil, not quite a flat plate, but pretty close, is used.

actually, stiffness is proportional to the square of thickness. Depth is akin to chord and a flat plate will still be floppy if chord is increased.

@PeterKämpf Thanks. Didn't want to get too mathematical so amended the wording to stress that I was talking about the thickness of the wing, not chord.

This is Stack Exchange, so we should assume that readers know things like time complexity and big O notation. And we know that O(n) is quite different from O(n²). In other words, it is not too mathematical for the audience here.

@PeterKämpf  Kay

Quite true, @PeterKämpf, but there are a lot of people on Aviation asking very basic questions with little to no knowledge of aviation. (For example, me, when I started here, and I still struggle with wing thickness & chord, though I haven't studied...)

the lift generation mechanisms of these two wing designs are quite different.
Insects use completely flat wings to great advantage. They generate both thrust and lift by shedding vortices in a flight regime in which the wing is operated right at the threshold of flow separation. Dragonflies operate there, and can accelerate from zero to 10 meters/second in one second or less, fly inverted, and execute unbanked turns at full speed.
Cambered wings are used by birds and airplanes and generate lift using (your choice) models based on vorticity and rotational flow, the bernoulli effect, or van Karman vortex shedding.

Interesting aspect: You compare both shapes in the respective domain where they are the best choice. Flat plates for viscosity-dominated flow and blunt airfoils for inertial-dominated flow.

@PeterKämpf yes yes, thanks for that insight! Most valiant!